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AFTER thousands of years of evolution, the social achievement that separates
humans from other animals is—the queue in a bank or a post office. Without
the cooperation of total strangers a queue would quickly break down. Researchers
have traditionally relied upon self-interest to explain why humans tend to
cooperate. Now, American anthropologists have shown that what keeps us toeing
the line is our tendency to mimic others, combined with the threat of
punishment.

What this new research means is that the traditional explanation is not true,
says economist Herb Gintis of the University of Massachusetts in Amherst.
“Basically, it’s a new way of getting at how human beings interact.”

Kinship and reciprocal altruism explain why animals such as bats, baboons,
bees and ants cooperate. Animals consistently cooperate with the same
individuals. The scale of cooperation among baboons, for instance, is the same
whether they are roaming the rainforests or living in captivity.

“But humans cooperate in larger groups. When humans go to war, for example,
they will cooperate with large numbers of individuals they are unrelated to and
probably won’t see again,” says anthropologist Joseph Henrich of the University
of Michigan in Ann Arbor, Michigan.

Humans show far greater variation than other animals. The Machiguenga people
in the Peruvian Amazon will only cooperate with their close kin, says Henrich.
But he points out that in modern nations people cooperate in their hundreds of
thousands.

Henrich and anthropologist Robert Boyd of the University of California in Los
Angeles looked at the transmission of culture among humans. “There are two
elements of human cultural psychology that we know about: one is that people
have a tendency to copy the majority, the other is that people have a tendency
to copy the most successful individual,” says Henrich. The two researchers
developed a mathematical model to explain how these tendencies promote
cooperation.

“What we are able to show is that because humans rely on copying the
successful and the majority, this creates a stable cooperative equilibrium which
doesn’t exist if those two cultural transmission mechanisms aren’t in place,”
says Henrich.

Because cooperation probably leads to more food, better health and economic
growth for the community as a whole, individuals in successful groups become
role models for outsiders. When enough individuals from other groups start
mimicking members of the successful group, the non-cooperative groups start
being nudged towards cooperation.

Genetic changes quickly back up this social movement. “Genetic evolution will
bring genes into the population that support the cooperative equilibrium,” says
Henrich.